Ultralow-dielectric, nanoporous poly(methyl silsesquioxanes) films templated by a self-assembled block copolymer upon solvent annealing

A homogenous, nanoporous poly(methyl silsesquixoxane) (PMSSQ) with a uniform pore size distribution was prepared by templating with a poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymer. The self-assembly of the PS-b-P4VP and PMSSQ precursor (PMSSQ-P) blends thin films was achieved by solvent annealing firstly; then the self-assembled thin films were thermally cured to prepare nanoporous PMSSQ films after removal of the PS-b-P4VP porogen. The influence of annealing solvent and PS-b-P4VP loading on the self-assembly behavior of the PS-b-P4VP/PMSSQ-P blends films were studied. By exposing to CHCl₃ vapor, fingerprint-type microphase-separated structures were achieved for the PS-b-P4VP/PMSSQ-P blends films with PS-b-P4VP loading ranging from 30% to 60%. The formation of the microphase-separated structures is attributed to the substantial mobility of the PS blocks and the P4VP/PMSSQ-P complexes, and segregated repulsion between them under the CHCl₃ vapor. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results demonstrated the prepared nanoporous PMSSQ films had a homogenous spherical pore morphology, with closed nanopores and a uniform size distribution over large areas. The porosity and dielectric properties of the homogenous, nanoporous PMSSQ could be adjusted by the content of PS-b-P4VP in the PS-b-P4VP/PMSSQ-P blends. As the PS-b-P4VP loading increased to 60 wt%, an ultralow dielectric constant of 1.41 was obtained, making the nanoporous PMSSQ films have potential applications in microelectronic devices.